1. Field of the Invention
The present invention relates to ink jet printing apparatuses that perform printing on print media in accordance with print data using an ink jet print head that ejects a colored liquid (ink) in droplet form. In particular, the present invention relates to ink jet printing apparatuses that automatically determine the optimum print mode on the basis of the type of paper or ink jet printing apparatuses that automatically determine the optimum ink ejection amount. The present invention also relates to methods for determining print media using any of these ink jet printing apparatuses and methods for determining ink ejection amount.
2. Description of the Related Art
The ink jet printing scheme forms images by ejecting a monochromatic ink or a plurality of color inks for color printing onto print media (paper, clothes, OHP paper, printed circuit boards, or the like). An ink jet printing apparatus employing this printing scheme generally comprises a carriage on which a print head and an ink tank are mounted, means for reciprocating the carriage, a conveying section that conveys print media, and a control section that controls these components.
Such an ink jet printing apparatus ejects ink droplets through a plurality of ejection ports (nozzles) while serially scanning the print head in a direction (main scanning direction) crossing (for example, substantially orthogonal to) a direction (sub-scanning direction) in which print media are conveyed. On the other hand, each print medium is intermittently conveyed in increments of a predetermined amount to allow the ink jet printing apparatus to print the print medium in accordance with the print data.
The ink jet printing scheme ejects ink directly onto a print medium in response to a print signal and is thus widely used as a simple, inexpensive printing scheme. The ink jet printing apparatus is not only used for a monochromatic ink but can also be adapted for full colors by providing a plurality of print heads for the respective color inks. Some full color type ink jet printing apparatuses comprise four types of print head for four colors, that is, three primary colors including yellow (Y), magenta (M), and cyan (C) as well as black (B), and further comprise ink tanks. Some full color type ink jet printing apparatuses comprise six types of print head for six colors, that is, the above four colors plus pale magenta (PM) and pale cyan (PC).
The conventional ink jet printing apparatus is disadvantageous in that ink attached to a print medium to form characters or images may dissolve into water to cause the printed characters to bleed. This has led to a demand for a technique for printing waterproof images that prevent the characters from being degraded. One such technique is a method of, before or after ink ejection, ejecting a treatment liquid to an ejection position for the ink on a print sheet in order to improve printability. With this method, for example, before ink ejection, a treatment liquid is ejected to the ejection position for the ink, at first. Subsequently, printing ink is ejected to the position to which the treatment liquid has been ejected. The two droplets mix on the print sheet to make it difficult to dissolve the ink into water. The treatment liquid has, for example, the property of being transparent and of fixing the ink on the print sheet.
On the other hand, some ink jet printing apparatuses can print a large number of print media such as ordinary paper, matte paper, and glossy paper. Some of these ink jet printing apparatuses execute print modes corresponding to the different types of print medium in order to perform printing operations appropriately corresponding to the types of print media. For example, some types of print medium require a relatively large amount of ink to achieve a high optical density, and the amount of ink required varies depending on the type of the print medium. Further, the time required to fix ink on the print medium varies depending on the type of the print medium. Thus, the ink jet printing apparatus can achieve a high image grade for each type of print media by performing printing in the print mode corresponding to the type of print media. Some of these ink jet printing apparatuses require users to select the type of print media for printing.
However, many users fail to recognize the necessity to select the print mode depending on the type of print media. The user simply depresses a “print” button to start a printing process. In this case, the printing apparatus executes printing in a print mode normally set by default (initial setting) or an already set print mode. If the executed print mode fails to correspond to the print media in an installed cassette, it causes problems such as the resulting image quality may disadvantageously be degraded. For example, the optimum print mode varies among ordinary paper, matte paper, and glossy paper.
The matte paper has high ink absorbing ability. Therefore, the matte paper causes insufficient optical density of pixels, resulting in a bluffed image, unless a larger amount of ink is ejected to the matte paper than to the ordinary paper. Further, owing to its absorptivity, the glossy paper may require a much larger amount of ink for bright colors. Moreover, some types of glossy paper require a long time for the ink to be absorbed by and fixed on the print medium. Therefore, in case of printing to glossy paper, it requires a longer time for the ink to be fixed on the print medium than case of printing to ordinary paper.
With the configuration in which the user selects the print mode, when, for example, the print mode for the glossy paper set in the printing apparatus during the last printing process remains set, the user may simply depress the print button without selecting the print mode again. In this case, if sheets of ordinary paper are stacked in a tray of the printing apparatus, the apparatus prints the ordinary paper in the print mode for the glossy paper. This causes a large amount of ink to be ejected, resulting in an increase in printing time as well as excessively dark and damp images. Further, in pixels in which different colors are adjacent to each other, the corresponding inks may run and mix to markedly degrade the image quality. Moreover, ink having failed to be absorbed by an ink receiving layer of the print medium may adhere to and thus contaminate the printing apparatus and adhere to the back surface the succeeding printed print medium on a discharge tray to also degrade the quality of the image on this print medium.
As described above, one of major causes of the degraded image quality is the failure to properly select the print mode according to the ink absorbing characteristic of print media.
In recent years, users' diversified demands have made many types of print medium with various characteristics commercially available from ink jet printing apparatus manufacturers and other venders. Thus, to obtain print matter with desired image quality, the user needs to select the optimum print mode (print medium type). However, the large number of print medium types has made it difficult for the user to select the optimum print mode. Consequently, the ink jet printing apparatus desirably senses the type of the print media stacked (or the ink absorptivity of the print media) to select the appropriate print mode, eliminating the need for the user to select the print mode.
In this regard, some ink jet printing apparatuses have a paper type sensor to recognize and check the material characteristics of print media against already memorized paper types to determine the type of the print media to automatically select the optimum print mode. For example, an ink jet printing apparatus described in Japanese Patent Laid-Open No. 11-235856 comprises a paper type sensor composed of a through-beam optical interrupter sensor. The through-beam optical interrupter sensor determines the type of the print media to in turn determine whether the print media are transparent sheets or opaque ordinary paper. If the print media are transparent sheets, the type is determined to be transparent sheets. Then, the optimum print mode is automatically selected depending on the detected print media.
An ink jet printing apparatus described in Japanese Patent Laid-Open No. 11-216938 exposes the print media to light to detect the gloss or color of the print media on the basis of reflected light to automatically correspondingly select a print medium type.
An ink jet printing apparatus described in U.S. Pat. No. 6,006,688 exposes the print media to light to measure the intensity of reflected light to determine the type of the print media to automatically select the optimum print mode.
The methods described in Japanese Patent Laid-Open Nos. 11-235836 and 11-216938 and U.S. Pat. No. 6,006,688 all simply determine the type of the print media on the basis of their optical properties. None of these methods determine the type of the print media on the basis of their ink absorptivity. Thus, if the print media offer similar optical properties but different ink absorption characteristics, the accuracy of determination of the print media is limited. As a result, the optimum print mode may not be selected.